Add option for outputting a deferred loading mapping.

pkg/compiler/lib/src/dart2js.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.cmdline;
 
 import 'dart:async'
     show Future, EventSink;
 import 'dart:convert' show UTF8, LineSplitter;
 import 'dart:io'
@@ skipping 315 matching lines @@
                           '--trust-primitives')),
     new OptionHandler(r'--help|/\?|/h', (_) => wantHelp = true),
     new OptionHandler('--package-root=.+|-p.+', setPackageRoot),
     new OptionHandler('--analyze-all', setAnalyzeAll),
     new OptionHandler('--analyze-only', setAnalyzeOnly),
     new OptionHandler('--analyze-signatures-only', setAnalyzeOnly),
     new OptionHandler('--disable-native-live-type-analysis', passThrough),
     new OptionHandler('--categories=.*', setCategories),
     new OptionHandler('--disable-type-inference', implyCompilation),
     new OptionHandler('--terse', passThrough),
+    new OptionHandler('--deferred-map=.+', implyCompilation),
     new OptionHandler('--dump-info', implyCompilation),
     new OptionHandler('--disallow-unsafe-eval',
                       (_) => hasDisallowUnsafeEval = true),
     new OptionHandler('--show-package-warnings', passThrough),
     new OptionHandler('--csp', passThrough),
     new OptionHandler('--enable-experimental-mirrors', passThrough),
     new OptionHandler('--enable-async', setEnableAsync),
     new OptionHandler('--enable-enum', passThrough),
     new OptionHandler('--allow-native-extensions', setAllowNativeExtensions),
     new OptionHandler('-D.+=.*', addInEnvironment),
@@ skipping 245 matching lines @@
   --disable-native-live-type-analysis
     Disable the optimization that removes unused native types from dart:html
     and related libraries.
 
   --categories=<categories>
     A comma separated list of allowed library categories.  The default
     is "Client".  Possible categories can be seen by providing an
     unsupported category, for example, --categories=help.  To enable
     all categories, use --categories=all.
 
+  --deferred-map=<file>
+    Generates a json file with a mapping from each deferred import to a list of
+    the part.js files that will be loaded.
+
   --dump-info
     Generates an out.info.json file with information about the generated code.
     You can inspect the generated file with the viewer at:
     https://dart-lang.github.io/dump-info-visualizer/
 
 '''.trim());
 }
 
 void helpAndExit(bool wantHelp, bool wantVersion, bool verbose) {
   if (wantVersion) {
@@ skipping 92 matching lines @@
       } else if (exitCode == 253) {
         print(">>> TEST CRASH");
       } else {
         print(">>> TEST FAIL");
       }
       stderr.writeln(">>> EOF STDERR");
       subscription.resume();
     });
   });
 }